Reagent dosing systems such as Selective Catalytic Reduction (SCR) dosing systems are used in vehicles to reduce emissions such as nitrogen oxide (NOx) in the exhaust gas flow.
A known SCR dosing system doses a reagent (reductant) such as urea into an exhaust gas flow. The urea is converted into ammonia which assists in converting NOX gases. The system comprises a urea tank, a urea delivery module (UDM), and a feed line which feeds urea to a urea injector. The UDM may be adjacent, or fitted to, the urea tank. The urea injector acts to inject urea into the exhaust line. The UDM may integrate various components and sensors, a pump, filter, heater, temperature sensor, quality sensor, and urea level sensor. Typically the injector is cooled via a cooling system where cooling fluid is passed e.g. in a jacket around the injector. So, urea is delivered from the urea tank, via the UDM and the feed line to a dosing injector module comprising a solenoid injector.
Typically urea (dosing) injector comprises a solenoid operated urea injector which includes an actuator coil; such injectors typically operate in a similar fashion to fuel injectors.
The injector may be provided with a cooling system i.e. by passing a cooling fluid such as water adjacent to the injector e.g. via a cooling jacket. So, in known SCR dosing systems, pressurised urea is supplied to the (dosing) injector which may be fluid (e.g. water) cooled.
Reductant (urea) injectors may become blocked. Thus there is the potential of a failure due to an injector developing blocked nozzle orifices, due to e.g. deposits of urea crystals or exhaust deposits developing thereon. In such cases, the injector current profile, that is the current across the urea injector coil terminals is not affected, as the injector valve moves in the usual fashion. Thus, when trying to determine if injector nozzle have become blocked, one cannot rely on detection of this via detection of valve movement.
Some urea/reductant supply systems may be able to detect lack of flow there through; however most systems are unable to detect the lack of flow due to blocked nozzles/orifices.
It is an object of the invention to determine problems with reductant (e.g. urea) injection. It is a further object of the invention to provide an indication of blocked nozzles in a reductant (urea) injector.